Patent GB-499588-A (GB)
Title: Improvements in and relating to telephone installations
IPC: H04Q3/00
Filed: 1937-06-25
Abstract: 499,588. Automatic exchange systems. LEHNER, C., GADESMANN, M., LEICHTHAMMER, K., and LEICHTHAMMER, H., (trading as TELEFONBAU UND NORMALZEIT LEHNER & CO.)..June 25, 1937, No. 17795. Convention date, June 26, 1936. [Class 40 (iv)] In a system employing junctions which are inductively-coupled to the repeaters at either end, the talking circuit in each repeater is normally open and is completed when the called party replies, so that speech currents cannot interfere with the alternating current control signals over the junction during the setting up of the call. After the talking circuit is established, the control signals take the form of code impulses, which in the system described, are sent by means of a stepping switch and are received by a chain of relays, although synchronous distributers may also be employed. Establishment of call. Upon seizure of the repeater Ue1, relay C energizes in series with A(i), which is then short-circuited, an A.C. impulse being sent over the junction. Sluggish relays Q, U energize, and Q falls back. Relay F(i) is connected through A(ii) to the a wire during the operating period of U and these relays operate to battery thereon if the call is set up by an operator. Relay F(ii) locks and the momentary operation of A(ii) sends a second A.C. impulse. If battery is connected to the a wire with Q, U both up Bes energizes and applies battery to the b wire to effect busy release. In the incoming repeater Ue2, the first impulse is received by J, AR and brings about the operation of CR, E and the seizure of the next selector. Sluggish relays QR, UR energize, and QR falls back. The second impulse, if received while QR is up, connects up FR which locks and applies battery to the a wire to adapt the selectors for toll working, FA being operative in the final selector LW. Impulses over the a wire are repeated by A(ii), and B(i) operates at each impulse and connects B(iii) in place of A(ii), so that the outgoing impulses are of limited length. The impulses are repeated over the a wire by J, AR in the repeater Ue2, VR being energized during each train. In the event of a busy condition, weak current through resistance Wi14 operates MR over the b wire, and a long A.C. impulse is sent back by SR during the release period of NR. This operates W, H, Y, and weak current through resistance Wi2 is applied to the b wire to give a, busy signal. When the connection is released at the calling end before conversation, relays C, U falls back and A(iii) sends a long A.C. impulse over the junction during the relapse of U to release CR by short-circuiting. If the wanted line is idle, PA energizes while UA is still up and weak current on the b wire operates MR to send an A.C. impulse which is cut off by the release of UA. In the repeater Ue1, W, H, Y operate and at the end of the impulse Y holds in series with X which earthes the b wire to give an idle signal, and connects up T. Upon reply, YA applies strong current through resistance Wi15 to the b wire to operate K and a short A.C. impulse is sent by SR during the operating period of LR, which connects up TR to complete the talking circuit and switch in the amplifier V3. In the repeater Ue1, W H respond and disconnect X, Y, whereupon G energizes, completes the talking circuit and switches in the amplifier V2. On an ordinary call the current in the b wire is cut off by ZA after a short interval, whereas on a toll call it is maintained since FA is up. The operation of G in the latter case connects battery to the b wire since F is up to give a signal to the operator. Release of an ordinary call. When the calling party hangs up, relays C, U fall back, whereupon relays L, S pull up and disconnect G, T. Relay L acts as a stepping relay for advancing the switch SS which in various positions connects up A(iii) to send a code release signal, which in the present instance consists of two short impulses followed by two long ones. In the repeater Ue2 these result in the operation of a set of two-step relays OR, PR, RR, WR. The length of the short impulses is checked by NR, UR, which fall back if they are too long, and the length of the long impulses is checked by XR, YR, which have not time to fall back if they are too short, while VR ensures correct spacing of the impulses. If the signal is correctly received, CR is short-circuited and UR, TR, NR, E fall back. Relay K energizes over offnormal contact on of the next selector and sends back a short A.C. impulse which operates X, Y to maintain the guard on the repeater Ue1 and disconnects S to stop the release signal. A further A.C. impulse when contact k opens disconnects X, Y. The code release signal is repeated until an impulse is received back, and an alarm is given if S remains up for an abnormal time. Should it be desired to delay release until metering impulses have passed between the exchanges, a relay connected to the a wire is employed to disconnect G and send a different signal combination which brings about the release of TR but not of CR. Release then takes place later in the manner described above. Supervision on toll call. When the called party hangs up, the relapse of YA disconnects K, LR, TR and a switch SSR steps under the control of BR in a manner similar to SS to send a code signal consisting of two long impulses followed by two short ones. This is received by a set of two-step relays O, P, R and G is disconnected, battery being removed from the b wire to signal the operator. The called party may be re-rung by the transmission of a single impulse. When the operator clears, a long impulse is sent over the junction to release CR, as in the case of release before conversation. Breaking in on busy line. The operator sends an impulse over the a wire to A(ii) and a similar impulse is sent over the a wire in the repeater Ue2 to effect switch-through. In order to sever an existing local connection, a further impulse is applied to the a wire to connect up L and the code release signal is sent as described above. Since FR is up, this results in the release of TR and battery is applied to the a wire to interrupt the existing connection. The re-operation of YA restores the talking connection.